1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device, a semiconductor device, a display device and an electronic instrument.
2. Related Art
As a method of forming a film with a predetermined pattern on a substrate, an etching method using a mask composed mainly of resin has been widely used (See JP-A-5-338184, for example.).
Specifically, the patterned film is obtained on the substrate by the following steps. I: A layer, which is composed of a material for forming the film, is formed on the substrate. II: A resist material is applied on the layer. III: A resist layer having openings corresponding to unnecessary portions of the layer is obtained by exposing and then developing the resist material. IV: Using the resist layer as a mask, the portions of the layer exposed inside the openings by an etching method. V: The mask is then removed.
However, according to the above method, it is time-consuming and troublesome to form the resist layer. As a result, problems such as a long time required for forming the film or increase in cost have arisen.
As the measure for solving such problems, in resent years, there is proposed a method of forming a film with a predetermined pattern by selectively supplying (dropping) areas for forming the film with droplets including a film material using a droplet ejecting method such as an inkjet method.
However, when the droplets are supplied on the substrate, the supplied droplets tend to spread on to wet the surface of the substrate in normal substrates, which do not absorb the droplets. Therefore, if a film with an elongated shape is to be formed, those having line widths larger than the diameter of the landed droplet can only be obtained in general.
As a method of reducing spreading and wetting, a method of increasing lyophobicity of the substrate against the droplets is also studied. However, in this case, the droplets supplied on the surface of the substrate form aggregated substances to decrease the superficial areas, namely to maintain the droplet shapes even on the substrate. Therefore, it has a strong tendency that the film with an even thickness cannot be obtained, or that breaking occurs in the middle of the film.
Taking the above into consideration, in forming the film having an elongated shape using the inkjet method, there is a limitation in a control of resolution of the film, in other words, a control of the width of the film as the case stands.
Meanwhile, in recent years, organic thin film transistors using organic materials (organic semiconductor materials) presenting electrically conductive properties similar to semiconductors are under development. The organic thin film transistors have advantages of good adaptability to low-profile and weight-saving, flexibility, low material cost and so on, and are expected to realize switching elements for flexible displays or the like.
As the organic thin film transistor, there is proposed one having a source electrode and a drain electrode formed on a substrate and an organic semiconductor layer, a gate insulating layer, and a gate electrode stacked on the electrodes in this order, which can be manufactured using an evaporation method or a coating method such as an inkjet method described above.
Although it is proposed that an inkjet method is used for forming the gate electrode of the organic thin film transistor, the line width of the gate electrode to be obtained tends to be too large in this case because of the reason described above (See JP-T-2003-518754, for example.).
And, if the line width becomes too large, the area of an overlapping section of the gate electrode and the source electrode increases, thereby problematically increasing the parasitic capacitance. Further, if the organic thin film transistor is used as a pixel transistor for a drive board of a display device, problems of a low aperture ratio and low display quality caused in accordance with the line width of the gate electrode arise.